# alignment in align-env: what is aligned in what way?

In this example:

\begin{align*}
& \lim( \neg ( \Sigma^* a_1 \Sigma^* a_2 \dotsb a_n \Sigma^* ) ) & = & \{ \alpha \in \Sigma^\omega | \exists^\omega n : \alpha [0,n] \notin \Sigma^* a_1 \Sigma^* a_2 \dotsb a_n \Sigma^* \} \\
& & = & \{ \alpha \in \Sigma^\omega | \forall n: \alpha [0,n] \notin \Sigma^* a_1 \Sigma^* a_2 \dotsb a_n \Sigma^* \} \\
& & = & \neg \ext( \Sigma^* a_1 \Sigma^* a_2 \dotsb a_n \Sigma^* )
\end{align*}


There is a huge space between \lim( \neg ( \Sigma^* a_1 \Sigma^* a_2 \dotsb a_n \Sigma^* ) ) and =.

Why? How can I avoid that? I actually want to have the = right next to it, as if I wouldn't have used &.

You're not using the align* environment correctly: There's way too many &s in your code. You need only one & before the = sign:

\documentclass{article}
\usepackage{amsmath}
\DeclareMathOperator\ext{ext}
\begin{document}
\begin{align*}
\lim( \neg ( \Sigma^* a_1 \Sigma^* a_2 \dotsb a_n \Sigma^* ) )
&= \{ \alpha \in \Sigma^\omega | \exists^\omega n : \alpha [0,n] \notin \Sigma^* a_1 \Sigma^* a_2 \dotsb a_n \Sigma^* \} \\
&= \{ \alpha \in \Sigma^\omega | \forall n: \alpha [0,n] \notin \Sigma^* a_1 \Sigma^* a_2 \dotsb a_n \Sigma^* \} \\
&= \neg \ext( \Sigma^* a_1 \Sigma^* a_2 \dotsb a_n \Sigma^* )
\end{align*}
\end{document}


Note that a few more things could be improved in your code: The outer parentheses of the \lim could be larger (use \bigl( and \bigr)), and the {|} of the two sets could be larger, too (use \bigl\{, \bigm| and \bigr\}).

• That looks good, except one detail: I have several other align environments in this parts and I want them all to start with the same left indentation. It seems that it is centered now which is not what I want. – Albert Mar 16 '11 at 14:22
• @Albert: I'll be glad to answer your other question if you provide the details I asked for. My code above is just supposed to be an answer to your question here, and it is, isn't it? :-) – Hendrik Vogt Mar 16 '11 at 14:28
• The very first & I put there was so that the left indentation is the same as for other align blocks I have. In your code, it seems centered and other align blocks start with different left indentation. But I don't want that; I want that it always starts with the same left indentation. How? – Albert Mar 16 '11 at 14:38
• @Albert: As I said, I answered the question you asked here. Let's discuss this at your other question, where it's relevant! – Hendrik Vogt Mar 16 '11 at 14:45
• In my question, the indentation was actually more like what I wanted and in your answer, it is not at all anymore, that is why I haven't accepted it yet. :) It is now centered. I don't want it to be centered. Or does align always centers the content? How can I avoid that? And all this is I think unrelated to the other question. But maybe not. I'm not sure. I still haven't really understood how align works and how it does the alignment. That is why I was asking here. :) That was actually more the question than just another solution. Sorry if I was unclear. – Albert Mar 16 '11 at 14:58